JPH077612U - Ceramic vertebral body prosthesis - Google Patents

Abstract

(57) [Abstract] [Purpose] A ceramic vertebral body prosthesis, which is inserted between the upper and lower vertebral bodies in place of the resected intervertebral disc during discectomy surgery, which increases the compressive load resistance and prevents bone resorption, To obtain minimal vertebral bone resection, ease of insertion, stability after insertion, etc. [Structure] A ceramic vertebral body prosthesis in which the surfaces that come into contact with the vertebral bodies are each formed of a contact curved surface that is convex outward.

Description

[Detailed description of the device]

[0001]

【Technical field】

 The present invention relates to a ceramic vertebral body prosthesis that is inserted between upper and lower vertebral bodies in place of the resected intervertebral disc during discectomy surgery.

[0002]

[Prior art and its problems]

 Nerve roots may be compressed due to disorders of the intervertebral disc such as the cervical spine, resulting in various neurological symptoms. As the treatment, local rest and fixation, and conservative treatment such as traction therapy are given, but if pain does not improve or the disability is significant, surgical treatment is given. There are two types of surgery: one is to remove the affected intervertebral disc from the anterior vertebral body, and the other is to remove the hernia by partially removing the vertebral arch from the posterior vertebral body. The method of cutting the intervertebral disc from the anterior side is called anterior fusion because bone fixation is performed between the upper and lower vertebral bodies that have become voids.

In this anterior fusion, autologous iliac bone is often used as the bone to be transplanted, but the secondary invasion due to iliac harvesting imposes a heavy mental and physical burden on the patient. Therefore, in recent years, a method of implanting artificial materials such as ceramics instead of the autologous iliac bone has been adopted. It is said that ceramics generally exist stably in a living body and have high compatibility with the living body.

However, while ceramics have high biocompatibility, they have the properties of being brittle and hard, and weak against physical shock. The vertebral body prosthesis must have mechanical strength to withstand the compressive load received from the upper and lower vertebral bodies, at the same time it does not cause bone resorption in the upper and lower vertebral bodies, and interposes soft tissue between the prosthesis and the bone. Instead, direct contact or fusion with the bone is required.

Since it is necessary to excise a part of the upper and lower vertebral bodies according to the shape of the vertebral body prosthesis, the vertebral body prosthesis preferably has a shape that minimizes bone resection. . However, the ceramic vertebral body prostheses currently in use are focused only on increasing the strength of the material itself and the compressive load, and their shape has not been sufficiently taken into consideration. Nor was there any consideration to minimize bone resection.

Further, when inserting a vertebral body prosthesis between the vertebral bodies, the prosthesis is inserted with the upper and lower vertebral bodies spread out. He could not expect to widen his body distance, and spent a lot of time in surgery because he relied on pushing apart the upper and lower vertebral bodies by a separate means.

[0007]

[The purpose of the device]

 The present invention is based on the above-mentioned awareness of problems regarding conventional vertebral body prostheses, increases compression stress resistance, eliminates vertebral body bone resorption, minimizes vertebral body bone resection during surgery, and facilitates insertion. Furthermore, the purpose is to improve the stability in the inserted state.

[0008]

[Outline of the device]

 The present invention was made as a result of research on the shape of a ceramic vertebral body prosthesis.Therefore, focusing on the fact that the contact surface of the vertebral body with the intervertebral disc is macroscopically concave, a disc to be inserted in place of the intervertebral disc is inserted. On the contrary, if the body prosthesis is composed of the convex surface corresponding to this concave surface, increase in compressive load, prevention of bone resorption, minimization of vertebral bone resection, easy insertion, stability after insertion, etc. are achieved at once. It was completed by finding out what will be done. That is, the present invention is characterized in that, in a ceramic vertebral body prosthesis that is inserted between the upper and lower vertebral bodies with the intervertebral disc removed, the surfaces that come into contact with the upper and lower vertebral bodies are composed of curved surfaces that are convex outward. I am trying.

As described above, when the upper and lower surfaces of the vertebral body prosthesis are curved outwardly, it is possible to withstand a compressive load received from the upper and lower vertebral bodies. In addition, the contact surface of the vertebral body with the prosthesis is concave on a macroscopic scale, and therefore the cut-out portion that is cut along the convex curved surface is minimal. Moreover, the contact surface between the vertebral body and the prosthesis is a shape that combines irregular curved surfaces, so this prosthesis not only bears the compressive load in the vertical axis direction of the vertebral body, but also slightly deviates from the axial direction. It is possible to withstand the lateral force by dispersing the stress. When viewed from the side of the vertebral body that is in contact with the prosthesis, bone resorption is prevented by the distribution of stress, which prevents sinking of the vertebral body prosthesis. It is possible to function without causing deformation.

The contact curved surface of the present vertebral body prosthesis with the vertebral body may be composed of a curved surface having a single curvature, or may be composed of a complex curved surface composed of a plurality of curved surfaces having different curvatures. For example, the curvature of the curved surface of the cross section perpendicular to the insertion direction and the curvature of the curved surface of the parallel cross section can be different from each other.

Particularly, considering the ease of inserting the vertebral body prosthesis, it is preferable that the front part in the insertion direction is gradually thinned. That is, the wedge shape is preferable only for ease of insertion, but as described above, it is preferable that the entire surface is a curved surface. If a curved surface with a small curvature on the side and a curved surface with a large curvature on the rear side are combined, both the ease of insertion and the construction of a curved surface can be satisfied.

Alumina, zirconia, calcium phosphate-based ceramics and the like are suitable as the ceramics used in the vertebral body prosthesis of the present invention. In particular, calcium phosphate-based ceramics are more preferable because they can be expected to have bone fusion with the vertebral body and enable firm fixation. As the calcium phosphate ceramics, hydroxyapatite, tricalcium phosphate, etc. can be adopted.

Further, the vertebral body prosthesis of the present invention is more preferably made of porous calcium phosphate ceramics having a true porosity of 30 to 55%. In the case of a porous body, osteoblast invasion into the stomata on the contact surface with the vertebral body allows for earlier bone fusion and faster functional recovery. The porosity is preferably 30 to 55% as true porosity. If it is less than 30%, the amount of pores is small and it cannot be expected to contribute to bone formation. If it exceeds 55%, the mechanical strength will be poor, and it will not be able to withstand the compressive load and cannot be used.

A method for manufacturing a ceramic vertebral body prosthesis of the present invention will be described by taking a hydroxyapatite ceramic as an example. A hydroxyapatite slurry is obtained by wet synthesis from a phosphate and a calcium salt by a known method. The resulting slurry is dried using a rotary drum dryer or the like to obtain hydroxyapatite powder. This powder is formed into a ceramic vertebral body prosthesis shape of the present invention by, for example, a dry hydrostatic press. The formed body is fired in an electric furnace in the range of 1000 to 1200 ° C to obtain a vertebral body prosthesis. In addition to this, as a molding method, a method of casting a slurry, an injection molding method, a method of forming a green compact and laminating it, and the like can be used.

The above method is a method for obtaining a dense vertebral body prosthesis having a true porosity of 10% or less within the above range. However, in the case of obtaining a porous vertebral body prosthesis having a true porosity of 30% or more. For the above, a foaming agent and water are added to the above hydroxyapatite powder, and the mixture is thoroughly stirred and the slurry containing bubbles is dried to obtain a dried body. The dried body is processed into a ceramic vertebral body prosthesis shape of the present invention with a milling lathe or the like, and baked in an electric furnace at a temperature of 1000 to 1200 ° C to obtain a vertebral body prosthesis. In addition to this, as a manufacturing method, a method in which flammable beads are added to the powder, followed by molding and firing to obtain pores in the bead portion can be adopted.

Further, the vertebral body prosthesis of the present invention may be composed of a ceramic having a dense central part and a porous peripheral part. The dense body in the central part mainly acts to increase mechanical strength, and the porous body in the peripheral part acts to promote bone fusion with the vertebral body. Such a porous ceramic with a central dense periphery is made by, for example, forming a central part with a dense dry body and a peripheral part with a porous dry body, and firing (shrink fitting ), Or a method in which the dried body of the dense body and the dried body of the porous body are adhered to each other with a slurry of apatite and the mixture is baked as it is. The present invention is characterized by the shape of the vertebral body prosthesis, and the manufacturing method is not limited to the above method.

[0017]

[Example of device]

 The present invention will be described below with reference to illustrated embodiments. 1 to 3 show an example of the shape of a ceramic vertebral body prosthesis 10 according to the present invention. The ceramic vertebral body prosthesis 10 has a substantially rectangular shape in plan view, like the cross-sectional shape of the vertebral body (cervical vertebra or thoracolumbar vertebra). The ceramic vertebral body prosthesis 10 has a symmetrical shape with respect to a vertical centerline (center plane), and has contact curved surfaces 12 that are convex outwardly on the upper and lower surfaces of the central wedge-shaped portion 11, respectively.

Assuming that the insertion direction between the vertebral bodies is A, the central wedge-shaped portion 11 of the ceramic vertebral body prosthesis 10 is formed so that the front side in the insertion direction is slightly thin in a cross section parallel to the insertion direction A. There is.

The contact curved surface 12 has a small curvature curved surface 12a with a small curvature (large curvature radius) on the front side in the insertion direction and a large curvature (curvature on the rear side) in the cross section in the direction parallel to the insertion direction A. It is composed of a large curvature curved surface 12b (having a small radius). The curved surface of the cross section in the direction orthogonal to the insertion direction A is composed of one curved surface in each cross section.

As shown in FIG. 4, the ceramic vertebral body prosthesis 10 having the above structure is inserted between the vertebral bodies 20 with the small curvature curved surface 12 a in front. The small curvature curved surface 12a has a smaller curvature (larger radius of curvature) than the large curvature curved surface 12b, and the central wedge-shaped portion 11 is thin on the front side in the insertion direction, so that the upper and lower vertebral bodies 20 are spread by the wedge action as a whole. You can insert while. After the insertion, the contact curved surface 12 constitutes a contact curved surface that is convex outward from the small curvature curved surface 12a and the large curvature curved surface 12b as a whole, so that the compressive stress from the vertebral body 20 is dispersed, It does not resorb and sits stably between the vertebral bodies 20. Macroscopically, the size of the excised part on the side of the vertebral body 20, which is concave, is minimal.

In the illustrated example, the central wedge-shaped portion 11 is slightly wedge-shaped, and combined with the convex curved surface of the contact curved surface 12, the effect of easier insertion can be obtained. Instead, it may have a simple parallel plane shape. Further, the vertebral body prosthesis 10 in the illustrated example has an advantage that it does not need to be selected from above and below because it has a symmetrical shape with respect to the center line in the upward and downward directions. However, it may be vertically asymmetric depending on the surgical case.

Next, a specific manufacturing example will be described. [Example 1] A hydroxyapatite slurry was wet-synthesized by a known method. The obtained slurry was dried with a rotary drum dryer manufactured by Nishimura Iron Works Co., Ltd. to obtain hydroxyapatite powder. This powder was calcined in an electric furnace at 800 ° C. for 3 hours as a handling treatment. The calcined powder was metal-pressed to form a cylindrical green compact having a diameter of 35 mm and a length of 35 mm. Furthermore, a pressure of 1 ton / cm ² was applied to the obtained green compact by a hydrostatic press to obtain a cylindrical green compact having a mechanically processable strength. This green compact was processed into various dimensions having the shapes shown in FIGS. 1 to 3 by taking into account the amount of shrinkage during firing, and fired at 1100 ° C. for 2 hours in an electric furnace to obtain a vertebral body prosthesis. It was This vertebral body prosthesis was used as an anterior fusion bone graft in several patients with disc herniation and good results were obtained.

Example 2 A hydroxyapatite slurry obtained by a known wet synthesis method was dried by a rotary drum dryer manufactured by Nishimura Iron Works Co., Ltd. to obtain a hydroxyapatite powder. This powder was calcined in an electric furnace at 800 ° C. for 3 hours as a treatment for handling. Powdered ovalbumin (100 g) was added to calcined hydroxyapatite powder vertebral body (200 g), gently mixed with a dry ball mill, water (500 g) was added to the mixed powder, and the mixture was bubbled for 15 minutes with a hand mixer. It was transferred to a glass sheath having a depth of 5 cm and dried in a dryer at 80 ° C. for 24 hours to obtain a porous dried body. This porous dried body was cut into a rectangular parallelepiped shape, processed into various dimensions having the shape shown in FIGS. 1 to 3 by an NC lathe and a milling machine in consideration of the firing shrinkage rate, and then heated in an electric furnace at 1200 ° C. for 3 hours. Firing was performed to obtain a vertebral body prosthesis. This vertebral body prosthesis was used as an anterior fusion bone graft in several patients with disc herniation and good results were obtained.

[0024]

[Effect of device]

 As described above, according to the present invention, the compression stress is high, there is no bone resorption in the vertebral body, the bone resection of the vertebral body during surgery is minimal, the insertion is easy, and the stability in the inserted state is high. A ceramic vertebral body prosthesis can be obtained.

[Brief description of drawings]

FIG. 1 is a plan view showing an embodiment of a ceramic vertebral body prosthesis of the present invention.

FIG. 2 is a front view of FIG.

FIG. 3 is a right side view of FIG.

FIG. 4 is a schematic diagram showing a state in which the vertebral body prosthesis of FIGS. 1 to 3 is inserted between vertebral bodies.

[Explanation of symbols]

 10 Ceramic Vertebral Body Prosthesis 11 Central Wedge 12 Contact Surface 12a Small Curvature Surface 12b Large Curvature Surface 20 Vertebra

Claims (5)

[Scope of utility model registration request] 1. A ceramic vertebral body prosthesis to be inserted between upper and lower vertebral bodies from which an intervertebral disc has been removed, wherein the surfaces that come into contact with the upper and lower vertebral bodies are each formed of a curved surface that is convex outward. Vertebral prosthesis. 2. The ceramic vertebral body according to claim 1, wherein the curved surface of contact with the vertebral body has a curvature of a cross section perpendicular to the insertion direction and a curvature of a curved surface of a cross section parallel to the insertion direction. Prosthesis. 3. The curved surface shape of a cross section parallel to the insertion direction of the contact curved surface according to claim 1 or 2, comprising a combination of a curved surface with a small curvature on the front side in the insertion direction and a curved surface with a large curvature on the rear side. Ceramic vertebral body prosthesis. 4. The ceramic vertebral body prosthesis according to claim 1, wherein the ceramic is calcium phosphate ceramics. 5. The ceramic vertebral body prosthesis according to claim 1, wherein the ceramic has a true porosity of 30 to 55%.